What is this control called?

Can anyone tell me what this control is called (see the red arrow in the image below)? And having once clicked it and made that section of the control panel disappear, is there anyway to undo the action, and get that part of my screen back?



It breaks free the menu and makes it a floating one.

Edit: If you just Alt-Tab around you should see that window. If not just rename/remove your .ardour2 directory and it’ll reappear

Thanks peder, that helps. On my Mac OSX 10.5.4 I couldn’t Alt-Tab and find the hiding window, but when I moved the remaining part of the window, I found the edit tools were concealed underneath. Once I found it, the downward pointing angle had turned into an upward pointing angle. I guess I could call this an “undock” and “dock” button? Thanks for your help. Mystery solved.

Yep pretty much got it;)